Last update: November 19, 2010 11:26:50 AM E-mail Print

 

Determining the relationship between staple strength and production

and subjectively assessed wool traits

 

M.J. Herselman, W.J. Olivier and M.A. Snyman

 

Grootfontein ADI, P/Bag X529, Middelburg (EC), 5900

Corresponding author:  Tino Herselman

 


Staple strength (SS) is the second most important factor in determining the price of wool, owing to its effect on the processing of wool. SS is to a large extent affected by environmental factors, such changes in feeding, season, reproduction status and illness. The increased demand for finer wool has lead to an increase in the selection intensity for decreased fibre diameter. A major problem with this is the fact that finer wool types tend to have a lower SS compared to strong wool types. The purpose of this study was therefore to quantify the genetic correlations and relationships of SS with the production traits included in the Small Stock Improvement Scheme, as well as certain subjectively assessed wool traits. Data collected on the 2000 to 2004 born lambs from the Cradock fine wool Merino stud (CM), Grootfontein Merino stud (GM), Carnarvon Afrino stud (CA) and Grootfontein Dohne Merino stud (GD) were used for this study. The production traits analysed included body weight (BW), clean fleece weight (CFW), mean fibre diameter (MFD), staple length (STPL) and coefficient of variation (CV). For the CM, GM and CA the following subjectively assessed traits included were wool quality (Qual), variation over the fleece (Var), bellies and points (B&P; CM) and creeping belly (CB; CA). The heritabilities of SS were 0.48±0.13, 0.23 ± 0.09, 0.34±0.06 and 0.31±0.06 for CM, GM, CA and GD respectively. The genetic correlations (rG) between SS and BW were 0.21±0.14, 0.10±0.16 and 0.25±0.30 for CM, CA and GD respectively. The respective rG for CFW were 0.30±0.14, 0.22±0.13 and 0.04±0.31 and for MFD 0.49±0.11, 0.05±0.12 and 0.59±0.17. The rG between SS and STPL and CV were 0.10±0.16, 0.22±0.13 and 0.23±0.27 and -0.67±0.08, -0.29±0.12 and -0.78±0.11 respectively. From the relationships between the EBV’s for the different traits, it is evident that for one unit increase in the EBV of BW (kg), CFW (kg), MFD (kg) STPL (mm) and CV (%), the EBV of SS changed by 0.41, 4.20, 2.16, -0.04 and –1.49 kTex/Nm for CM, 0.02, 4.79, 1.13, 0.24 and –0.60 kTex/Nm for CA and 0.06, 5.97, 2.17, 0.08 and –2.12 kTex/Nm for GD. The fact that staple strength is not incorporated in the breeding plans of wool sheep breeds in South Africa may pose a risk as the data of this study suggest that selection for fineness might have a negative effect on staple strength.